LT1952
21
1952f
APPLICATIO S I FOR ATIO
WUU
U
Figure 16. 36V to 72V Input to 12V at 20A No ‘Optocoupler’ Synchronous ‘Bus Converter’
Figure 15. LT1952-Based Synchronous ‘Bus Converter’ Efficiency
vs Load Current (For Circuit in Figure 16)
48V to Isolated 12V, 20A (No Opto-Coupler)
‘Bus Converter’
The wide programmable range and accuracy of the LT1952
Volt-Second clamp makes the LT1952 an ideal choice for
‘Bus Converter’ applications where the Volt-Second clamp
provides line regulation for the converter output. The 48V
to 12V 20A ‘Bus Converter’ application in Figure16 shows
a semi-regulated isolated output without the need for an
optocoupler, optocoupler driver, reference or feedback
network. Some ‘Bus Converter’ solutions run with a fixed
50% duty cycle resulting in an output variation of 2-to-1
for applications with a 72V to 36V input range. The LT1952
uses an accurate wide programmable range Volt-Second
clamp to initially program and then control power supply
output voltage to typically ±10% for the same 36V to 72V
input range. Efficiency for the LT1952-based bus con-
verter in Figure 16 achieves a high 94% at 20A (Figure 15).
LOAD CURRENT (A)
4
EFFICIENCY (%)
96.0
95.5
95.0
94.5
94.0
93.5
93.0
10 12 1486 161820
1952 F15
V
IN
= 48V
V
OUT
= 12V
The solution is only slightly larger than 1/4 “brick” size and
uses only ceramic capacitors for high reliability.
•
••
••
LTC3900
8V
BIAS
V
U1
V
U1
220pF
8V
BIAS
3
FG
5
CG
V
IN
36V TO 72V
T1
PA0815.002
BAS516
BCX55
V
OUT
12V, 20A
10k
10k
10k
C
T
1nF
1µF
R
T
15k
560Ω
L1: PA1494.242 PULSE ENGINEERING
T1: PULSE ENGINEERING
T2: COILCRAFT
C
OUT
33µF, 16V
X5R, TDK
3x
0.1µF
2.2µF, 100V
2x
1nF
BAT760
12V
Si7370
2x
PH4840
2x
18V
T2
Q4470-B
82k
47k
1952 F16
2.4µH
SD_V
SEC
OUT
LT1952
714
R
OSC
V
IN
315
BLANK GND
98
SS_MAXDC PGND
513
DELAY
12
V
REF
OC
611
COMP I
SENSE
110
FB SOUT
216
•
PH21NQ15
2x
1
GND
6
CS
+
2
V
CC
4
CS
–
7
SYNC
8
TIMER
370k
9mΩ
1µF
470Ω
39k
13.2k
115k
27k
0.47µF
0.1µF
10k59k
12V Bus Converter Efficiency
